This invention relates to mechanical load brakes, and more particularly to a self-adjusting mechanism for a load brake, to compensate for wear of surfaces of the brake due to friction.
A mechanical load brake as commonly used in a hoist or other lifting device, dissipates the potential energy due to lowering the load by converting the kinetic energy produced by lowering the load into heat, through friction. The friction causes wear of the brake friction surfaces. Adjustments to the brake to compensate for the surface wear are normally required to provide proper operation and long life of the brake. Means to permit the renewal of the friction surfaces without extensive dismantling of the braking system are desirable. Wear of the friction surfaces should be compensated if undue movement of the brake-actuating mechanism is to be avoided as the wear increases. The subject invention provides automatic adjusting means which are particularly adapted for this purpose.
Previous load brakes required manual adjustment. In previous devices, as the friction discs wear, an operating gap (for example, in some devices the distance between a driving lug with the brake clamp shut and a control pin) must be reduced by rotating the drive lug closer to the control pin. This adjustment, or similar adjustments in other devices, requires manual intervention which takes time, and the device cannot be used while the adjustment is being made. Furthermore, unless the operator was attentive to the need for adjustment, the brake reliability may become dangerously low.
The present invention provides a device which allows a brake to adjust automatically without downtime. The present invention maintains an optimal operating gap without the need for the operator to constantly check the brake surface wear.
One preferred embodiment of the present invention uses a one-way wrap spring which snugly fits on the load brake shaft. A tang of the wrap spring engages a drive hole in the input gear of the brake. The direction of the helix of the wrap spring is such that when the input shaft is turned in the "up" direction, the spring loosens its grip on the shaft. This permits the input gear to close as far as necessary to close the brake for "up" operation. In the "down" direction, the input gear turns on the shaft until the side of the drive hole strikes the wrap spring tang. This tightens the spring on the shaft and forces the shaft to turn with the input gear. The diameter of the drive hole is selected so the clearance of the tang within the drive hole corresponds to the optimal operating range. The wrap spring moves around the shaft as the discs wear maintaining the optimal adjustment for the brake. In addition to a helical wrap spring, other one-way devices may be adapted for use in the present invention.
The foregoing invention will become more apparent when viewed in light of the accompanying drawings and the following description wherein: